Demethylation of Waste Alkali Lignin for Rapid and Efficient Ammonia Adsorption

Alkali lignin, a significant waste resource from the pulp and paper industry, is produced in large quantities each year, but its utilization remains limited. This study focuses on the cleavage of -OCH3 groups attached to the aromatic ring in alkali lignin to obtain demethylated alkali lignin nanospheres (DAL-NPs) enriched with aromatic hydroxyl (Ar-OH) groups. These DAL-NPs are intended for the efficient adsorption of NH3. Qualitative and quantitative characterization of alkali lignin, both pre- and post-demethylation, was performed using Fourier transform infrared spectroscopy and 1H NMR. The analysis revealed a reduction in methoxy groups and an increase in Ar-OH groups in the DAL-NPs. The NH3 adsorption experiment demonstrated that the DAL-NPs exhibited a rapid and high adsorption capacity, reaching an NH3 uptake capacity of 10.0 mmol g(-1) within 0.42 min at 298 K and 1.0 bar. In addition, the DAL-NPs displayed superior selectivity based on the ideal adsorption solution theory for 10% NH3/90% N-2 (3252) and 10% NH3/90% CO2 (175) at 298 K and 1.0 bar. The DAL-NPs also demonstrated reversibility and stability during 10 adsorption-desorption cycles. The DAL-NP adsorbent possesses exceptional properties, such as abundance and low cost, rapid and efficient adsorption, reversibility, and stability, making it a promising solid adsorbent for effective NH3 adsorption in the ammonia process.